The source of amino acids in parenteral nutrition is generally the amino acid in its free crystalline form. Aluminum is a contaminant in amino acids, and therefore, in parenteral solutions. Indeed, the Food and Drug Administration is considering proposing regulations regarding aluminum content of parenteral solutions. Large volume parenterals may need to be certified for an upper limit of aluminum and small volume parenterals may need to be labelled for aluminum content. In addition, environmental and health concerns dictate that even low levels of aluminum may be undesirable.
Accordingly, there exists a need in the industry to easily and effectively quantify the amount of aluminum in amino acids on a parts-per-billion basis. Most methods proposed for aluminum determinations have poor sensitivity at low levels of aluminum. Graphite Furnace Atomic Absorption Spectrometer detection is currently utilized for low level aluminum detection, however, the equipment is expensive and the results obtained often are not reproducible.
The application of high-performance liquid chromatography (HPLC) has been suggested to quantify aluminum levels. Specifically, salicylaldehydebenzoyl-hydrazone (SAB) has been disclosed as an HPLC pre-column derivatizing agent. A resultant highly fluorescent aluminum-SAB chelate is separated on a LiChroCART RP-18 column with an acetonitrile-water eluent containing tetrabutylammonium bromide, disodium EDTA and sodium acetate. In this manner, aluminum ion in water, and reagent alkalihydroxide pellets (LiOH, NaOH and KOH) were determined.
Similarly, 2,2'-dihydroxyazobenzene derivatives have been disclosed as reagents for trace metal determination in coal fly ash by ion-pair reversed-phase high performace liquid chromatography with spectrophotometric detection.
However, the prior art methods involving HPLC can introduce aluminum contamination, which leads to inaccurate results. At the low levels of aluminum involved, even trace amounts of contamination become significant.
It is therefore an object of the present invention to provide an improved method for determining aluminum at the parts per billion level by HPLC. The method is particularly applicable in quantitatively assaying for low levels of aluminum in amino acids in parenteral solutions.